1. Field of the Invention
The present invention relates to a projector that projects projected light onto a projection object such as a screen, and displays an image, and specifically relates to a projector which is equipped with a zoom lens which is able to change the size of the projected light range for which projected light is projected and with an imaging unit that senses an image of the projection object.
2. Description of the Related Art
In recent years, known projectors include those for which a zoom lens is equipped as the projection lens, and by driving that zoom lens and changing the zoom position of that zoom lens, the size of the projected light range formed on the screen can be varied freely.
Also, when installing this kind of projector in front of the screen, so that a suitable image will be displayed on the screen by the projected light that is projected from the projector onto the screen, it is necessary to make various adjustments such as zoom adjustment, keystone correction, and focus adjustment, etc. for the projector.
However, in the case of portable projectors, because there is a possibility of the relative position to the screen changing when the projector is installed, the user had to make the various adjustment noted above each time, which was very troublesome.
In light of this, in the past, for example as noted in Japanese Patent Laid-Open Gazettes No. 2000-241874, in addition to providing a monitor camera on the projector, when the projector is placed in front of a screen, first, at the projector, an adjustment pattern image formed on the liquid crystal light valve is enlarged and projected for display on the screen, the screen that displays this pattern image is sensed by the monitor camera, the sensed image is analyzed, and the various adjustments noted above were made to be automatically performed based on the analysis results.
Generally, with the monitor camera, there is provided a CCD (Charge Coupled Device) etc. that converts the incident light into electrical signals, and to set the overall brightness of the sensed image to a preset value (exposure target value), there is a function (auto exposure) for varying things such as shutter speed, gain (sensitivity) and aperture.
FIGS. 8(A) and (B) are explanatory diagrams for explaining the effect of auto exposure of the monitor camera for the prior art. In FIG. 8, the upper level shows a screen on which is displayed the adjustment pattern image, the middle level shows the sensed image that was obtained by sensing the screen using the monitor camera, and the lower level shows the value that shows the brightness of each pixel aligned along the center horizontal line (dotted line). Also, (A) shows the normal state of the projector, and (B) shows the state of the projector when set to low luminance.
Note that the value that shows the brightness of each pixel for the sensed image is called the gradation value hereafter. The concerned gradation value is a value that is obtained from image signals of the sensed image output from the monitor camera (CCD module).
In FIG. 8, the adjustment pattern image formed on the liquid crystal light valve is an all white image, and as shown in the upper level, in the screen, the range for which the pattern image is displayed, in other words, the white colored range, is the aforementioned projected light range.
Also, the sensed image obtained by sensing using the monitor camera is as shown in the middle level.
Also, in the lower level, the horizontal axis corresponds to the position of each pixel on the central horizontal line of the sensed image, and the vertical axis shows the gradation value of each pixel.
At the projector, when the light source lamp is set to low luminance, compared to during normal times, the luminance of the projected light projected from the projector is lower. Because of this, as shown in FIG. 8(B), the brightness of the pattern image displayed on the screen is darker than that during normal times shown in (A). However, when that pattern image is sensed with auto exposure by a monitor camera, even if the subject is dark, shutter speed, gain, or aperture, etc. are adjusted so as to correct the overall brightness of the sensed image, so as shown in FIG. 8 (B), the brightness of the pattern image is not different from the normal times shown in (A). Therefore, for the sensed image, the dark part (in other words, the part outside the projected light range) is dark to a negligible degree, so in comparison to the gradation value of each pixel for the black part being regarded as 0, the gradation value of each pixel for the white part (in other words, the pattern image part) almost doesn't change at all, and is left at the desired gradation value Lt.
In this way, by working the auto exposure function at the monitor camera, at the projector, the light source lamp is set to low luminance, and even if the brightness of the pattern image displayed on the screen becomes dark, for the sensed image, it is possible to maintain the gradation value of each pixel for the white part (in other words, the pattern image part) almost at the desired gradation value Lt the same as during normal times. This is not limited to times when set to low luminance, but is also the same in cases when there is a degradation over time of the light source lamp, so that the luminance decreases.
However, for a projector equipped with this kind of zoom lens and monitor camera, when the zoom position of the zoom lens was changed and the size of the projected light range on the screen was changed, there were the following kinds of problems due to the monitor camera auto exposure.
FIGS. 9(A) to (C) are explanatory diagrams that explain problems due to the monitor camera auto exposure when the zoom position is changed with the prior art. In FIG. 9, as with FIG. 8, the upper level shows the screen on which the adjustment pattern image is displayed, the middle level shows the sensed image of that screen, and the lower level shows the gradation value of the pixels for that sensed image. Also, (A) shows the state when the zoom lens zoom position is in the middle position, (B) shows the state when that zoom position is set to the wide angle side, and (C) shows a state when that zoom position is set to the telephoto side.
For the projector, when the zoom lens zoom position is set to the wide angle side, as shown in the upper level of FIG. 9(B), the area of the projected light range on the screen is wider than in the middle position of (A). Here, since the adjustment pattern image formed on the liquid crystal light valve is constant, when the area of the projected light range on the screen becomes wider, in accordance with this, the pattern image displayed on the screen also is enlarged. Therefore, when that pattern image is sensed by the monitor camera, for that sensed image, as shown in the middle level of FIG. 9(B), the area of the white part (in other words, the pattern image part) becomes wider than the middle position of (A), and the area of the black part (in other words, the part outside the projected light range) becomes narrower.
At this time, when that sensing is performed using auto exposure, the overall brightness of the sensed image is calculated as the exposure calculation value, and to make that exposure calculation value equivalent to a preset exposure target value, the shutter speed, gain, or aperture, etc. are controlled. Here, the overall brightness of the sensed image is a sum total of volume of the light detected with each pixel for the CCD converted to electrical signals and amplified, and that value is proportional to the average value of the gradation value of each pixel for that sensed image. Thus, normally, the exposure calculated value uses the average value of the gradation value of all pixels for the sensed image.
Meanwhile, since the exposure target value is a preset fixed value, as shown in FIG. 9(A), when the zoom position is the middle position, if we assume that the exposure calculation value matches the exposure target value, as described above, when the zoom position is put to the wide angle side and the area of the white part for the sensed image becomes wider, the average value of the gradation value of all pixels, in other words, the exposure calculated value, also rises above the exposure target value by the amount that the area became wider. As a result, when the auto exposure is operated, when the shutter speed, gain, or aperture, etc. are changed so that the exposure calculated value is equivalent to the exposure target value, the average value of the gradation value for all pixels for the sensed image decreases. As described above, for the sensed image, the black part is dark at a negligible level, and the gradation value of each pixel for the black part is regarded as 0, so as shown by the lower level in FIG. 9(B), the fact that the average value of the gradation value of all pixels decreases can be nothing other than the gradation value of each pixel for the white part decreasing to be lower than the desired gradation level Lt.
Conversely, when the zoom lens zoom position is on the telephoto side, as shown in the top level of FIG. 9(C), the area of the projected light range on the screen becomes narrow compared to the middle position of (A). Here, as described above, since the pattern image formed on the liquid crystal light valve is constant, when the area of the projected light range on the screen becomes narrow, along with this, the pattern image displayed on the screen is reduced. Therefore, when that pattern image is sensed by a monitor camera, for that sensed image, as shown by the middle level of FIG. 9(C), the area of the white part (in other words, the pattern image part) becomes narrower than the middle position of (A), and the area of the black part (in other words, the part outside the projected light range) becomes wider.
In this way, when the area of the white part for the sensed image becomes narrow, the average value of the gradation values of all the pixels, in other words, the exposure calculation value, decreases to lower than the exposure target value by the amount that the area became narrower. As a result, when the auto exposure is operated so as to change the shutter speed, gain, or aperture, etc. so that the exposure calculation value is equivalent to the exposure target value, the average value of the gradation values of all the pixels for the sensed image increases, and as a result, as shown by the lower level in FIG. 9(C), the gradation value of each pixel for the white part rises to higher than the desired gradation value Lt.
As explained above, with the prior art, when the zoom lens zoom position is set to the wide angle side and the area of the projected light range on the screen becomes wider, due to the monitor camera auto exposure, the gradation value of each pixel of the white part for the sensed image drops to lower than the desired gradation value Lt, and conversely, when set to the telephoto side and the area of the projected light range becomes narrower, the gradation value of each pixel of the white part rises to greater than the desired gradation value Lt, and in either case, it was not possible to maintain the average value of the gradation values of the white part at the desired gradation value Lt.
Therefore, in this way, when the average value of the gradation values of the white part for the sensed image departs from the desired gradation value Lt due to changes in the zoom lens zoom position, after that, as described above, that sensed image is analyzed, and based on the results of that analysis, when an attempt is made to perform various adjustments automatically, depending on the adjustment contents, there was the problem of not being able to perform suitable adjustments.
Note that this kind of problem can also occur in cases when the adjustment pattern image, not just when the whole surface is white, but is another specific color (e.g. green, etc.) other than white, or in cases when it is not the whole surface but rather part.